@Iceray: you said "@Orathaic I disagree with [religion] being a more recent invention. Caste system is a great example..."
A caste system does not require a religion. Just as marxism was insipred by contemporary atheist writers, it is possilbe to imagine a religion which dictates a purely communal/communist economy (and, say, a ban on charging interest for lending money as christianity once did) that system would be capable of all the same destruction which the Communist party of Russia did without nay reference to God.
Arguably any system of ideas/strategies* could be framed as a religion or as a purely atheistic ideology - thus any social grouping could, by the way you are arguing, potentially be called a religion. You would then be arguing that humans by their very nature are religious. That humans by their very nature come up with religious ideas - it is like you're arguing against religion by accepting it is fundamental to human nature.
I would argue that humans are capable of 'evil' as, defined by our morale values, for other reasons, and that religion does not hold the monopoly on violence or war. I would probabaly concede that religion can be used as a means of control - controlling thoughts and behaviour - and that this in and of itself is firstly not unique to religion, and secondly can be a net benifit to society. (though with our current level of communication technology it is possible that individuals thinking from themselves - unlimited by religion or any other controls over what they think about - could produce more benifit to society, just as a free market allows innovation wihout the direction/control of government...)
*Strategies - being ways of acting, economic, social, morale, whatever... but overall any successful society usually uses some sort of strategy to prevent, say, theft which would harm society as a whole while benifitting the individual thief. Religion may be a used in many places to encourage enforcement of such strategies...